Charge pump is a kind of capacitive voltage converter which can be used to raise or lower a voltage, or even be used to generate a negative voltage. As charge pump circuits are capable of high efficiencies while being electrically simple circuits, they have been widely used in single-supply-powered integrated circuits, such as electrically erasable programmable read-only memories (EEPROM's) and flash memories. A charge pump can increase a power supply voltage and thereby converts it to a high-voltage signal for driving a load or supporting read and write operations of an EEPROM or a flash memory.
FIG. 1 schematically illustrates a common charge pump circuit of the prior art. The charge pump circuit includes a charge pump 101, a regulator circuit 102, a capacitor C1 and a load current I1. FIG. 2 shows a schematic diagram showing a waveform output from the charge pump circuit of FIG. 1. It can be seen from FIG. 2 that, as the charge pump circuit of FIG. 1 only applies some simple filtering to an output voltage of the charge pump 101 and is lack of ripple control, there are great ripples in the output waveform. Therefore, the charge pump circuit cannot output a relatively stable voltage, thus being unfavorable for a downstream integrated circuit.